Color linear charge coupled device and method for driving the same

ABSTRACT

A color linear charge coupled device for an image pickup apparatus includes red, green, and blue photo diode arrays. First, second, third and fourth transfer gates formed in the device move signal charges generated at the photo diode arrays toward first, second and third horizontal charge coupled device (HCCD) shift registers. By controlling the transfer gates, the red and green signal charges are first transferred to their HCCD shift registers. The blue signal charge is then transferred to its HCCD shift register. Only three HCCD shift registers are required, thus, the device dimension and configuration is considerably simplified compared to prior art configurations. Also, the color resolution of the device is greatly improved because the distance between the respective photo diode arrays is substantially decreased.

This is a division of application Ser. No. 08/670,099, filed Jun. 25,1996, now U.S. Pat. No. 5,751,032.

BACKGROUND OF THE INVENTION

The present invention relates to a color linear charge coupled devicefor an image pickup apparatus, and, more particularly, to a color linearcharge coupled device (CCD) for improving color resolution by reducingthe distance between the respective pixels, and a method of driving thesame.

A conventional color linear CCD will be described with reference to FIG.1, a schematic diagram of the conventional color linear CCD.

Each row of the CCD includes photo diode arrays 1, 2 and 3; transfergates 5 positioned at both sides of photo diode arrays 1, 2 and 3;horizontal charge coupled device (HCCD) shift registers 4 surroundingthe outer side of transfer gates 5; a floating diffusion element (FD) 7positioned at one side of each CCD array; and a sensing amplifier 8connected to FD 7.

The operation of the conventional color linear CCD will now bedescribed. When transfer gate 5 is turned on, signal chargesphotoelectrically converted in each photo diode of the respective photodiode arrays 1, 2 and 3 move through their transfer gates 5 and to HCCDshift registers 4. The signal charges are moved either to their upperHCCD shift register or to their lower HCCD shift register based on theposition of the charges' photodiode. In particular, the charges aremoved in a zigzag manner such that charges from odd numbered photodiodesmove to their upper HCCD shift register and charges from the evennumbered photodiodes move to their lower HCCD shift register (orvice-versa).

Subsequently, the charges in the shift registers are moved to the rightby clock signals applied to HCCD shift registers 4 so that the signalscan be sensed and extracted by FD 7 and sensing amplifier 8.

In summary, the red, the green and the blue linear CCD arrays have thesame configuration and operate in the same manner, except for theircolor. Thus, the conventional color CCD requires two HCCDs, one FD, andone sensing amplifier for each row that senses a color--a less thancompact design, which therefore increases the expense of the CCD. Also,because two transfer gates and two HCCDs are positioned in the spacesbetween the red, green, and blue CCD rows, the physical space betweenthe respective CCD rows is large, thus deteriorating vertical colorresolution.

SUMMARY OF THE INVENTION

To solve the problems of the conventional color linear CCD, it is anobject of the present invention to provide a color linear CCD suitablefor improving the color resolution by reducing the distance between therespective pixels and a method for driving the same.

To accomplish the above object, there is provided a color linear CCDcomprising a semiconductor substrate of a first conductivity type and awell region of a second conductivity type, formed on the firstconductivity type semiconductor. A photo diode array includes a reddetecting photo diode array formed in the second conductivity type wellregion, a blue detecting photo diode array, and a green detecting photodiode array, the blue and green photo diode arrays separately formed ona first side of the red detecting photo diode array. The photo diodearrays generate signal charges by photoelectric conversion. A horizontalcharge coupled device (HCCD) shift register portion has first and secondHCCD shift registers, each separately formed on a second side, oppositethe first side, of the red detecting photo diode array and a third HCCDshift register formed on the first side of the red detecting photo diodearray. Finally, the linear CCD includes a first, second, third, andfourth transfer gates for moving signal charge.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail a preferred embodiment thereofwith reference to the attached drawings in which:

FIG. 1 is a schematic diagram of a conventional color linear CCD;

FIG. 2 is a schematic diagram of a color linear CCD according to thepresent invention;

FIG. 3 is a vertical sectional view of the color linear CCD according tothe present invention;

FIGS. 4a-4e are potential profiles of the color linear CCD at varioustimes, according to the present invention; and

FIGS. 5a-5b are timing charts of the color linear CCD according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 2 and 3, the color linear CCD according to the presentinvention includes a first conductivity type semiconductor substrate 31and a second conductivity type well region 32 formed on the firstconductivity type semiconductor substrate 32. A red detecting photodiode array 23, positioned in the central area of second conductivitytype well region 32, generates signal charges by photoelectricconversion proportional to the amount of incoming red light. Similarly,a blue detecting photo diode array 24 and a green detecting photo diodearray 25 are situated to one side of red detecting photo diode array 23.HCCD shift registers 20 and 21 are positioned on the other side of photodiode array 23. Shift register 20 receives the signal charges generatedby the red photo diode array 23 and shift register 21 receives thesignal charges generated by the blue photo diode array 24. Another HCCDshift register, shift register 22, is situated to one side of greendetecting photo diode array 25 and receives the signal charges generatedin green detecting photo diode array 25.

Transfer gates 26a, 26b, 26c, and 26d move the signal charges generatedat the photo diodes by application of an ON/OFF signal. Transfer gate26a moves signal charges from photo diode 25 to shift register 22.Transfer gate 26b moves signal charges from photo diode 24 towards shiftregister 21. Transfer gate 26c moves, at separate times, signal chargesgenerated by photo diodes 23 and 24. Finally, transfer gate 26d movessignal charges from photo diode 23 to shift register 20.

Storage gate 34 is positioned on red detecting photo diode array 23 andcontrols the movement of the charges generated at blue detecting photodiode array 24. In particular, when a DC bias is applied to storage gate34, the potential of red detecting photo diode array 23 drops below thatof blue detecting photo diode array 24, and consequently, signal chargeflow between photo diode 24 and shift register 21 is possible.

Output gates 28a, 28b, and 28c; FDs 29a, 29b and 29c; and sensingamplifiers 30a, 30b and 30c are formed on one side of HCCD shiftregisters 20, 21 and 22. Poly gates 33a and 33b are repeatedly formed asshown, over the HCCD shift registers 20, 21 and 22, to serially shiftthe signal charges toward the output gates 28a, 28b, and 28c. Thetransfer gates 26a, 26b, 26c, and 26d, and the storage gate 34 are alsopoly gates. Signals in the shift registers 20, 21, and 22 are seriallyshifted using the poly gates 33a and 33b, until they are sensed andextracted by FD 7 and sensing amplifier 8.

Channel stop layer 27 is formed by implanting high-concentrationimpurity ions of a second conductivity type in the separated area of therespective cells for isolation of the photo diode cells of therespective photo diode arrays 23, 24 and 25.

The operation of the present invention will now be described withreference to FIGS. 4 and 5.

At time t0, the signal charges photoelectrically converted in therespective photo diode arrays 23, 24, and 25 are shown as areas 40, 42,and 44, respectively. At time t1, transfer gates 26a (TG1), 26c (TG3),and 26d (TG4) are turned on, thus reducing their respective potentialbarriers, causing the signal charge from photo diode array 25 (green)and 23 (red) to move into their respective shift registers. At time t2,transfer gates 26a, 26b (TG2), and 26d are turned off, raising theillustrated potential barriers. At time t3, transfer gate 26b is turnedback on, allowing signal charge from photo diode 24 to move into itsshift register 21. Finally, at time t4, all of the transfer gates areoff. Throughout the operation described in this paragraph, storage gate34 (STG) remains on, thus holding the potential of the red photo diodebelow that of the blue and green photo diodes.

Because there is a charge stopping layer 27 positioned between greendetecting photo diode array 25 and blue detecting photo diode array 24,signal charges are not mixed with each other.

After the signal charges generated at the photo diode arrays 23, 24 and25 are completely moved to HCCD shift registers 20, 21 and 22, clocksignals are applied to second and third poly gates 33a and 33b of HCCDshift registers 20, 21 and 22 to move the signal charges to the output.In FIG. 5b, the clock signals applied to poly gates 33a and 33b areshown as signals H01 and H02. After the transfer gates 26a through 26dhave finished switching, i.e., the signal charge has all beentransferred to the shift registers 20, 21, and 22, at time t5, clocksignals H01 and H02 are alternatively applied to poly gates 33a and 33b,as shown, to sequentially move the signal charges to the output gates28a, 28b and 28c.

In the present invention, blue detecting photo diode array 24 is placedin the center to prevent the absorption of red components when thesignal charges are moved to the HCCD shift registers 20 and 21 throughthe storage gate 34, improving the color resolution.

As described above, according to the color linear CCD of the presentinvention, the number of required HCCD shift registers is reduced,compared to conventional CCD arrays, considerably simplifying the deviceconfiguration and allowing improved color resolution because thedistance between the respective photo diode arrays.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope or spirit of the invention.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A method for driving a color linear chargecoupled device having a photo diode array portion having a red detectingphoto diode array formed in a predetermined area of said secondconductivity type well region, a blue detecting photo diode array, and agreen detecting photo diode array, the blue and green photo diode arraysseparately formed on a first side of said red detecting photo diodearray, the photo diode arrays for generating signal charges by aphotoelectric conversion; a horizontal charge coupled device (HCCD)shift register portion having first and second HCCD shift registers eachseparately formed on a second side, opposite the first side, of said reddetecting photo diode array and a third HCCD shift register formed onthe first side of the red detecting photo diode array; a first transfergate for moving signal charge; a second transfer gate for moving signalcharge; a third transfer gate for moving signal charge; and a fourthtransfer gate array for moving signal charge from said red detectingphoto diode array, said method comprising the steps of:moving the signalcharges generated at said red detecting photo diode array toward saidfirst HCCD shift register via said second HCCD shift register, andmoving the signal charges generated at said green detecting photo diodearray toward said third HCCD shift register by driving said first, thirdand fourth transfer gates; and turning off said fourth transfer gate,turning on said second transfer gate and moving the signal chargesgenerated at said blue detecting photo diode array toward said secondHCCD shift register via said red detecting photo diode array.
 2. Themethod for driving a color linear charge coupled claimed in claim 1,wherein clocks of said first, device as second and third HCCD shiftregisters are fixed while the signal charges are moved from saidrespective photo diode arrays toward said respective first, second andthird HCCD shift registers.